The present invention relates to a method of, and an apparatus for, measuring a pattern dimension using an electron beam, which is particularly suitable for the measurement of a distance between bottom edges of a fine pattern of a reversed taper shape.
In a conventional technique for measuring a pattern dimension using a secondary electron signal generated upon application of an electron beam to a pattern to be measured, various automatic measuring algorithms have been proposed for a pattern of a normal taper shape, such as a linear approximation method, a curve approximation method, a threshold method, a maximum inclination method, a difference method and the like. Such algorithms are selectively used, depending upon the material and shape of a pattern and the material of an underlying layer.
For a pattern of a reversed taper shape such as a line pattern having a larger top dimension than a bottom dimension or a space pattern having a smaller top dimension than a bottom dimension, the distance between the bottom edges has been determined from the distance between top edges or from the cross section obtained by cutting a specimen, because the bottom edges cannot be observed when a beam is applied vertically.
An automatic measuring algorithm, as conventionally used, can detect with high precision the distance between bottom edges of a normal taper shape pattern. However, for a reversed taper shape pattern, the distance between bottom edges cannot be measured if a beam is applied vertically. Manual measurement also allows measurement of only the distance between top edges. A reversed taper shape pattern is found, for example, in a negative type electron beam sensitive resist pattern, an Al-Si wiring pattern and the like. In the case of an Al-Si wiring pattern of a reversed taper shape, as the distance between adjacent patterns becomes short, the probability of generation of a "blowhole" increases during a manufacturing process for an interlayer insulator film. It is therefore necessary to quantitatively check the degree of reversed taper. It is, therefore, required to obtain not only the distance between top edges of a reversed taper shape pattern, but also the distance between bottom edges and a difference ratio (dimension reduction ratio) between the top edge and bottom edge distances.
It is possible to measure the degree of reversed taper by cutting a specimen and observing its cross section. However, it is necessary to break the specimen. In addition, it is difficult to quantitatively observe the cut section of a pattern if it is not exactly vertically cut relative to the pattern.